quipus

quipus or khipus (kēˈpōz) [key], groups of strings, knotted for tally, which were used by the Inca for keeping records and sending messages. The quipu, which is believed to have predated the rise of the Inca, was based on the decimal system. Small cords with knots in them were attached to a main cord or a top band; the color of the cord, its place, its size, and the knots in it were all of significance to the record or the message. The quipus had to be made up and deciphered by specially trained officials. The method of deciphering is not known today, although Andean shepherds still use a sort of quipu.